[Show abstract][Hide abstract]ABSTRACT: This paper analyzes the mass size distribution of some inorganic species present in the atmospheric aerosol from a field campaign carried out in Madrid throughout a complete year (February 2007–February 2008). Samplings were performed by means of a micro-orifice uniform deposit impactor (MOUDI). Ambient air was sampled during consecutive nocturnal and diurnal periods, and diurnal/nocturnal behaviors were compared for the twenty night-day sampling pairs that were gathered. Annual and seasonal averages were obtained, and some case studies under specific atmospheric conditions are discussed in the paper.Results have shown that the sulfate and ammonium mass was concentrated in the accumulation mode, between 0.18 and 0.56 μm, so that gas-phase and condensation processes for secondary aerosol formation prevailed during the sampling periods in this area. An exception to this behavior was found during a fog event when distributions for these two species were centered in the 0.56–1 and 1–1.8 μm size stages, corresponding to the droplet mode. In most of the samples, the ammonium mass measured in these size ranges was enough or almost enough to neutralize inorganic acidity by formation of ammonium sulfate and nitrate. However, a significant sulfate mass not neutralized by ammonium was found in the impactor backup quartz filter (aerodynamic diameter < 0.056 μm). The concentration of this sulfate and its contribution to the ultrafine fraction mass was higher under good dispersive conditions, prevailing in summer, when particle growth processes are not so favored due to the higher atmospheric dilution factors. The origin of this ultrafine sulfate has been attributed to direct emissions from traffic, associated to the nucleation mode.Regarding the nitrate concentration, it was found higher in the coarse mode than in the accumulation mode on an annual basis. The highest concentrations were measured in winter episodic situations. The marked seasonal variability shown in the accumulation mode by this species is related to the volatility of ammonium nitrate. Among all the studied ions, nitrate also presented the highest differences between the diurnal and nocturnal concentrations in all size ranges. This is probably related to the short time scale required for its formation from gaseous precursors.Highlights► Particulate nitrate, sulfate and ammonium are concentrated in the accumulation range. ► Particulate nitrate has a marked seasonal effect, with maximum value in winter. ► In-cloud sulfate formation and ammonium uptake was observed during a fog event. ► Ultrafine particles (<0.056 μm) were acidic due to a significant mass of sulfate.

[Show abstract][Hide abstract]ABSTRACT: The ambient particle number concentration and size distribution have been measured in an urban background site in Madrid, a continental Mediterranean area, over more than two years (Oct 2006–Dec 2008). The objective was to study the sources and processes affecting or contributing to fine and ultrafine particles in this area. They have been measured with a TSI–SMPS (15–600 nm) instrument and with a modified Vienna type DMA (3–80 nm) and a CPC 3025 (TSI) during 6 months. The average particle number concentration was lower than in other sites as it is an urban background site and because of its location in the Mediterranean area. The particle number concentrations have shown a clear seasonal influence: maximum values were observed every year in the period November–January, coinciding with atmospheric stagnant conditions and pollution episodes, while minimum values were measured in springtime, a period in which wind speed produced high atmospheric dilution. The Aitken and accumulation modes have shown similar seasonal behavior, with two maxima related to vehicle emissions. The nucleation mode had a third maximum observed at noon during spring and summer. The size distributions were bimodal during most of the time: the first mode was centered on 20–50 nm and was associated with fresh particles related to vehicle exhaust emission; the second mode, between 50 and 160 nm, mainly corresponded to the evolution of the first mode. The evolution of the size distributions reveals a marked annual cycle related to the season, with an increase of median diameters during summer and a decrease during winter. Different evolutions of particle size distribution corresponding to different meteorological and seasonal scenarios were identified. The influence of higher wind speeds on particle size distribution has been confirmed to cause a decrease in the particle number concentration and in the size distribution mode. Particle nucleation is not a frequent phenomenon in this measurement site, where 63 events per year have been observed. They mainly occurred during spring and summer periods, with the minimum number during winter. This suggests that insolation and temperature are important variables in nucleation. Class Ia nucleation events mainly occurred during spring and summer. High wind speeds were important during class II events, as the particles suffered low growth or lost their semivolatile compounds.

[Show abstract][Hide abstract]ABSTRACT: A time series of more than two years of continuous measurements of EC, OC and TC obtained with a Rupprecht and Patashnick (R&P) thermal analyzer at a suburban site in Madrid has been evaluated in this work. Correction factors obtained from intercomparison exercises with thermo-optical methods were applied to the original measurements. Corrected OC and EC mean values are 3.7 and 1.3 mu g m(-3) respectively. The highest individual values have been recorded in winter. No seasonal variation has been observed in OC, whereas a slight decrease of EC is observed in summer, leading to higher OC/EC ratios. The mean value of the OC/EC ratio is 4.9. Daily patterns show maximum EC and OC associated to traffic rush hours, with a delay of the OC peak related to the formation of SOC. Daily oscillation is more pronounced in winter. Hourly estimations of SOC production have been obtained by the primary OC/EC ratio approach, after discounting the OC, EC background contamination. A mean primary ratio value of 0.59 has been used for SOC short-term estimations throughout the entire time period. As expected, the highest SOC production is observed in summer, related to the increasing in photochemical activity, which also influences daily patterns and the time of the daily SOC maximum. In summer the daily SOC production ranges from 80 to 92%, whereas in the winter months it varies from 70 to 84%. These SOC estimations do not discount primary biogenic or natural contributions to OC and are therefore maximum values. (C) 2011 Elsevier Ltd. All rights reserved.

[Show abstract][Hide abstract]ABSTRACT: During DAURE 2009 winter field campaign, one of the sampling sites was Montseny, a rural background station located 40 km NNE from Barcelona and 25 km W from the Mediterranean Sea. It is a Natural Park and a protected area, thus with low human activity, mainly agriculture. The sampling station was located on a valley with it axis oriented on the direction NW-SE. At this site, a TSI-SMPS (DMA 3071 and CPC 3022) was installed in order to measure the particle number distribution in the size range 15-600 nm during the period March 19-27 with a measurement cycle of 12 minutes The particle mass distribution was measured by a micro-orifice uniform deposit impactor (MOUDI) using eleven size stages with aluminum substrates and a quartz fiber backup filter. Four samples were taken during the period 13-19 March, two during 24 hours and other two during 48 hours. This impactor has a wider size range allowing to measure from 56 to 18000 nm. The substrates and filters obtained were later analyzed for determining soluble ions (sulfate, nitrate, ammonium and calcium) by IC. There are mainly two different kinds of events measured with the SMPS. When the air masses were coming from SE, which meant that they could come from the park but also from the urban and industrial areas located in the pre-coastal depression, it was characterized by higher particle number concentrations and by size distributions centered on 80 nm. This meant it was an aged aerosol, which had grown up by coagulation, condensation and oxidation processes. When the air masses were coming from NW (the second valley axis side), the particle measured were much smaller, the instrument started to detect particles with 15 nm, but smaller ones could be possible. This meant that new particle nucleation could have occurred in the valley, just before arriving to the sampling point. From MOUDI samplings, two different types of events were also observed. Three of the four samplings coincided with stagnation of air masses or slight SE flows. During the 4th sampling, the air mass direction was oscillating, arriving from both possible axis sides. Comparing both situations, it was observed that there was not a big difference between them for sulfate and nitrate. Sulfate was found in the accumulation mode and in the backup filter, while nitrate also appeared in the coarse mode. Ammonium had a different behavior. It appeared in the accumulation mode and in the backup filter but not in the coarse mode during both kinds of events. When the air mass direction was oscillating, the ammonium concentration was much higher than during the other 3 samplings, more than enough to neutralize the sulfate and nitrate ions. In this case, the particulate nitrate observed in the coarse mode was neutralized by the calcium ion. Acknowledgement: Special thanks are given to X. Querol and A. Alastuey (IDAEA-CSIC) and J.L. Jimenez (U. Colorado, CO, USA) for organizing the DAURE field campaign. This part of the study has been financed by the CGL2007-3052-E/CLI, CGL2008-02817-E/CLI, PROFASE (CGL2007-64117) and GRACCIE (CSD2007-00067) projects. M.A. Revuelta acknowledges the Ministry of Science and Innovation for their economical support through the FPI predoctoral grant BES-2008-007079.

[Show abstract][Hide abstract]ABSTRACT: Inorganic compounds account for a significant mass of the ambient
aerosol. However this contribution varies with time and aerosol size
fraction, depending on the influence of source emissions and ambient
conditions, which can be relevant in the formation processes of
secondary species. Time series of particulate nitrate, 10 m time
resolution, have been obtained during the February-March and July 2009
DAURE (Determination of the sources of atmospheric Aerosols in Urban and
Rural Environments in the western Mediterranean) field campaigns in the
urban area of Barcelona by means of an R&P8400N monitor.
Meteorological conditions during these periods were relevant for the
photochemical formation and accumulation of secondary species. Ambient
concentrations were higher in winter, specially coinciding with
development of atmospheric stagnant episodes that enhanced the
accumulation of pollutants including particulate nitrate that reached
concentrations of 25 µgm-3 in some occasions, day or night, under
these conditions. High humidity periods favored in occasions the
formation of nitrates at submicronic scale. Variations in wind direction
resulted in transport of particulate nitrate from near emission areas.
Size segregated aerosol was sampled during the winter campaign with a
micro-orifice uniform deposit impactor (MOUDI) using eleven size stages
with aluminum substrates and a quartz fiber backup filter. Samples were
collected twice per day for day/night periods. The first sampling period
tried to collect secondary aerosol as it started after the early morning
emission period. The second sample collected the night aerosol and the
emission period. Soluble ions (sulfate, nitrate, ammonium and calcium)
were later analyzed by IC. The nitrate mass was concentrated in two
modes, the accumulation one around 0.75 µm and the coarse one
around 3.90 µm. The sulfate and ammonium masses were concentrated
in the accumulation mode, around 0.50 µm, although a small peak
close to 5 µm also appeared. The ammonium measured in the
accumulation mode was able to neutralize the inorganic acidity caused by
the nitrate and sulfate, but not the acidity in the coarse mode caused
by the nitrate. This particulate nitrate was generated by the reaction
of gaseous nitric acid with crustal calcium carbonate thus being calcium
the neutralizing cation. Acknowledgement: Special thanks are given to
the X. Querol and A. Alastauey (IDAEA-CSIC) and J.L. Jimenez (U.
Colorado, CO, USA) for organizing the DAURE field campaign This part of
the study has been financed by the CGL2007-3052-E/CLI,
CGL2008-02817-E/CLI, PROFASE (CGL2007-64117) and GRACCIE (CSD2007-00067)
projects. M.A. Revuelta acknowledges the Ministry of Science and
Innovation for their economical support through the FPI predoctoral
grant BES-2008-007079.

[Show abstract][Hide abstract]ABSTRACT: The improvement of air quality represents an important challenge for our
society. In urban areas, air quality standards are being exceeded. Like other
tropospheric pollutants, aerosols are presently under regulation in the European
Union. Control of aerosol concentration is an important objective, because high
levels can affect human health. As an indirect effect, aerosols can alter earth’s
radiative budget by scattering or absorbing radiation, producing a change of
ozone production. Because of both direct and indirect aerosol effects, it is
important to know aerosol levels in the troposphere.
Models can be used as a tool for air quality management. Secondary organic
aerosol (SOA) is presently one of the most important topics on air quality
modelling. Many aspects of SOA modelling are still a challenge for the scientific
community. Unfortunately, the quality of model results cannot be evaluated
because SOA measurements are not available at air quality stations. The reason
for that is that it is not possible to distinguish experimentally a primary organic
aerosol from a secondary one.
In this paper, an air quality model was used to simulate hourly SOA
concentrations during a 2003 summer period in the Madrid metropolitan area. A
simple reaction scheme for SOA was used. Modelled SOA was compared
against SOA estimations obtained from thermal OC and EC hourly
measurements at an urban background site, using the OC/EC minimum ratio
approach. Although a reasonable agreement is observed, higher-resolution
simulations with higher-resolution emissions should be carried out in order to
improve model predictions. Also, a more complex scheme of SOA formation
should be tested to determine the origin of the discrepancies.
Keywords: secondary organic aerosols, air quality modelling, organic carbon,
elemental carbon.

[Show abstract][Hide abstract]ABSTRACT: During the course of one year (March 2004–March 2005), PM2.5 particulate nitrate concentrations were semi-continuously measured every 10min at a Madrid suburban site using the Rupprecht and Patashnick Series 8400N Ambient Particulate Nitrate Monitor (8400N). Gaseous pollutants (NO, NO2, O3, HCHO, HNO2) were simultaneously measured with a DOAS spectrometer (OPSIS AR-500) and complementary meteorological information was obtained by a permanent tower. The particulate nitrate concentrations ranged from the instrumental detection limit of around 0.2μgm−3, up to a maximum of about 25μgm−3. The minimum monthly average was reached during August (0.32μgm−3) and the maximum during November (3.0μgm−3). Due to the semi-volatile nature of ammonium nitrate, peaks were hardly present during summer air pollution episodes. A typical pattern during days with low dispersive conditions was characterized by a steep rise of particulate nitrate in the morning, reaching maximum values between 9 and 14UTC, followed by a decrease during the evening. On some occasions a light increase was observed at nighttime. During spring episodes, brief diurnal nitrate peaks were recorded, while during the autumn and winter episodes, later and broader nitrate peaks were registered. Analysis of particulate nitrate and related gaseous species indicated the photo-chemical origin of the morning maxima, delayed with respect to NO and closely associated with secondary NO2 maximum values. The reverse evolution of nitrate and nitrous acid was observed after sunrise, suggesting a major contribution from HNO2 photolysis to OH formation at this time of the day, which would rapidly produce nitrate in both gaseous and particulate phase. Some nocturnal nitrate maxima appeared under high humidity conditions, and a discussion about their origin involving different possible mechanisms is presented, i.e. the possibility that these nocturnal maximum values could be related to the heterogeneous formation of nitrous and nitric acid by the hydrolysis of NO2 on wet aerosols.

[Show abstract][Hide abstract]ABSTRACT: An analysis of hourly measurements of gaseous pollutants and fine carbonaceous aerosol (PM2.5) divided into two fractions, elemental and organic carbon (EC and OC), in a suburban Madrid metropolitan area site is presented. Data were obtained using a semi-continuous thermal analyser for two periods of time during the summer and late autumn–early winter of 2003. In the summer period, correlation between EC and OC was poor (r=0.46), and high OC/EC ratios were usually found. In contrast, during the late autumn–early winter period the two carbonaceous aerosol fractions showed a high degree of correlation (r=0.94). Coincident peaks of OC and secondary gases (NO2+O3) were observed during summer episodes and also on some winter episodic days, suggesting a significant non-primary contribution to OC in fine aerosol, linked to photochemical oxidation of gaseous pollutants. OC apportionment between primary and secondary origins has been attempted for the two measuring periods using the EC tracer model. In the summer period, the results of this apportionment were very dependent on the y-intercept value (considered as the non-combustion OC background concentration) of selected linear regressions. Calculation of the secondary contribution to the OC fraction during polluted days gave diurnal maximum hourly estimations in a range from 35% to 55% and daily estimations averaged during the 10–19 h period ranging from 25% to 45%. Thus, this would confirm a daily urban photochemical origin for the secondary organic aerosol, although biogenic contribution to both the OC background and the SOA formation may be significant in the area during summer. During late autumn–early winter episodes primary contribution to OC was more prevailing, although the model also estimated maximum hourly values of secondary OC in the order of 35% of the measured OC.

[Show abstract][Hide abstract]ABSTRACT: Experimental vehicle idle emission factors have been compared with calculated factors for 100 vehicles in Madrid. The vehicles were selected according to the distribution (by age and fuel type) of the official, national car fleet (up to 31 December 1997). They were then clustered following the criteria of the Computer Programme to Calculate Emissions from Road Transport (COPERT III) category classification. NO(x) and CO idle emission factors show a wide range of values in each category and an important deviation between the experimental values and the corresponding parameterised ones. Fifteen percent of tested vehicles in this study have been identified as gross emitters generating approximately 50% of the total CO emission volume.

[Show abstract][Hide abstract]ABSTRACT: An experimental characterization of biogenic emission from Quercus ilex ssp. rotundifolia in a forest near Madrid, Spain, was carried out in the early autumn of the years 2000-2003. A dynamic branch enclosure technique was implemented to determine the monoterpene emission rates of this evergreen oak species during the 2000 and 2001 campaigns. Major compounds emitted during both measurement periods were limonene, alpha-pinene, beta-pinene, sabinene, and myrcene. In the 2000 field campaign the light- and temperature-dependent model of Guenther et al. [1993] did not fit the data due to drastic reductions of emission rates (and leaf gas exchange related parameters) observed at high air temperature and low air humidity (high water vapor pressure deficit). This plant physiological activity depletion and the subsequent emission reduction were attributed to severe water soil deficit conditions, as precipitation was very scarce during the growing season. In contrast, during the 2001 field campaign, neither emission nor physiological activity showed strong decreases in hot days. A good fit of experimental data to Guenther model was achieved in this field campaign (r2 = 0.90), and linear regression gave a standard emission factor (ES) of 14.0 mug gdw-1 h-1 (gdw is grams dry weight). Soil moisture was presumably higher than during the 2000 campaign due to recent rain events. With the purpose of documenting the drought stress effect at canopy level, monoterpene oak fluxes were measured by the modified Bowen ratio micrometeorological technique throughout the 2001 field campaign and in the late summer of 2002 and 2003. The measured emission by both techniques showed a reasonably good correlation, although micrometeorological fluxes were, in general, lower than upscaled branch emission rates. According to Guenther's parameterization, standard emission fluxes (FS) of 0.30 mug m-2 s-1 (r2 = 0.61) and 0.28 mug m-2 s-1 (r2 = 0.67) were derived for the 2001 and 2002 field campaigns, respectively. However, measured fluxes in September 2003 at high ambient temperature were much lower than those of the previous years. Moreover, from the CLCT range in which emission in this field campaign could be fitted to a linear behavior, the FS value obtained was 50% lower than the 2001 and 2002 values. Water xylem potential measurements indicated the existence of drought conditions during the 2003 campaign and unstressed water conditions during the 2002 campaign.

[Show abstract][Hide abstract]ABSTRACT: A great extension of Quercus ilex natural forest is found in the close vicinity to Madrid metropolitan area. This work presents the results obtained in a three-year field emission experimental study on this evergreen oak species (2000--02). Monoterpene emission has been documented during summer and early autumn seasons using a branch enclosure technique. Main features of this emission study focus on speciation, light and temperature dependence, and relationship with carbon assimilation and water stress. Severe soil water deficit induced a physiological depletion at high temperature in this sclerophyll and monoterpene non-storing oak species, reducing emission at minimum levels. In the opposite, if soil was enough wetted emission was reasonably well described by the isoprene model of Guenther although assimilation was reduced at high temperature. A field experiment designed to ascertain the role of air humidity on emission revealed no influence of this parameter under no soil water deficit conditions. Canopy emission fluxes were calculated from the modified Bowen-ratio technique using a micrometeorological tower deployed within the oak forest. A standard emission flux of 0.3 mug m-2s-1 according to the model of Guenther (30^oC and 1000 mumol m-2s-1 of PAR) was obtained (r^2= 0.67).

[Show abstract][Hide abstract]ABSTRACT: The results of a field study carried out in September–October 2000 near Madrid, regarding Quercus ilex and Pinus pinea monoterpene emission and its relation to ambient and physiological parameters, are presented in this paper. The major compounds in diurnal Q. ilex emission were limonene, α-pinene and β-pinene. Emission rates during warm days fitted reasonably well to the temperature and light-dependent model of Guenther (ES=13.4 μg gDW−1 h−1). However, during hot days at mid-day and afternoon hours, dramatic decreases of monoterpene emission, photosynthetic activity and stomatal conductance were observed. The poor soil–water availability combined with low relative humidity and high temperature is likely to be responsible for the observed emission drop. A parameterisation of emission, based on ambient atmospheric water vapour pressure deficit (WVPD), has been attempted in this study. Monoterpene diurnal emission from P. pinea was lower than that of Mediterranean oak (ES=1.5 μg gDW−1 h−1). A reduction in the total emission during the hottest hours of the day was not observed in this monoterpene storing species. Limonene emission rates, accounting on average for nearly half of the emission, were well described by the temperature-dependent model of Tingey. The rest of the emission was comprised of several compounds (cineole, myrcene, α-pinene, linalool) and was reduced at high WVPD values.

[Show abstract][Hide abstract]ABSTRACT: This paper describes the experimental potential of a classic ground-based passive remote sensing technique, the dispersive correlation spectroscopy (DCS), for the study of non-industrial urban plumes. The text presents this technique as an alternative tool to study some aspects of air pollution in cities, in contrast to the information supplied by air pollution monitoring networks. The results obtained with DCS in the study of Madrid plume in winter, one of the most important cases of urban pollution taking place in southern Europe, are presented here as an example of the DCS application. This highly inhabited zone, where pollutant emissions have essentially an urban origin, stays frequently under the influence of high-pressure systems, which strongly condition the efficient ventilation of the area and produce air pollution episodes of certain importance. The study presented here has been based on the previous technical improvement of the commercial COSPEC V instrument and on its use as a passive remote sensor from a mobile laboratory measuring NO2 total column. The formation process of the Madrid plume, its horizontal limits and the dynamics of transport are some of the aspects documented with this technique.

[Show abstract][Hide abstract]ABSTRACT: The main results of an experimental study focusing on the formation and transport of photochemical pollution in the Madrid air basin are presented. This southern European, heavily populated urban area is located on an elevated plateau at a height of 700 m, near a mountain range with maximum heights of around 2,400 m. Daily and seasonal cycles of ozone were documented during a one-year survey at three semi-rural sites located 30 km away from the urban center. Maximum hourly values of up to 140 ppb were measured, and the ozone generated within the urban plume on polluted days (when values exceeded 90 ppb) has been estimated at around 40-50 ppb.A meteorological characterization of these smoggy days pointed out the influence of thermally induced local wind flows on the concentration daily cycles at the measuring sites, denoting a preferred advection of the urban plume. Moreover, during intensive summer field campaigns, the use of meteorological and ozone sondes, as well as an instrumented aircraft, revealed some features about the horizontal and vertical distribution of the polluted air masses, as well as their evolution within the planetary boundary layer. Ozone plumes have been detected up to 100 km away from the city, usually mixed in a layer that reaches a height of 1,000-1,500 m in the afternoon. On some occasions, ozone-enriched layers have been detected as high as 4,000 m during morning hours, suggesting possible tropospheric injection induced by topographydriven flows or convective mesoscale systems that are usually present in the center of the Iberian Peninsula in the summer.